Disposable containers as multi-chamber containers or dual-chamber containers are frequently used in medicament delivery devices in order to facilitate the distribution of drugs to a patient. Dual-chamber containers comprise two longitudinally arranged chambers divided by a movable plunger arranged in the container. In one of chambers, normally the proximal chamber, a predetermined amount of freeze-dried drug is arranged while a diluent is arranged in the distal chamber. When a distal plunger is exposed to a pushing force, the diluent is transferred via a bypass passage to the proximal chamber where the diluent is mixed with the freeze-dried drug. When the distal plunger reaches the dividing proximal plunger, the distal chamber is completely empty and the mixture in the proximal chamber is ready for delivery. Continued proximal movement of the two plungers will deliver the mixture in the proximal chamber via a delivery member i.e. a needle, a nozzle, a mouth piece, etc. to the patient.
Unfortunately, there is a risk that a small amount of the mixture is encapsuled in the bypass passage and may flow back, distally via the bypass passage before the opening of the bypass passage is completely closed by the distal plunger. If the medicament delivery device is held in a vertical position with the delivery member pointing upwards, which is the normal position during preparation of medicament delivery devices i.e. injectors, inhalers, etc. the leaking mixture could continue flowing distally downwards along the plunger rod to the driving mechanism and affect the mechanism adversely. Leakage may sometimes also occur during use of conventional single-chamber containers but not as often as when dual-chamber containers are used.
There is consequently a need for an improved medicament delivery device that can be used over a long period of time together with disposable containers without risking adverse effects from fluids leaking from the containers.